Process of making cellulose esters of carboxylic acids



Patented Oct. 4, 1932 UNITED STATES PATENT OFFICE HANS T. CLARKE AND CARL 3', MALE, OF ROCHESTER, NEW YORK,-ASSIGNORS TO EAST- MAN KODAK COMPANY, OF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK PROCESS OF MAKING CELLULOS E ESTEZBS F CABIBOXYLIC A CIDS No Drawing.

This invention relates to processes of mak- I lose esters of many different organic acids,

even those of high molecular weight, may be. prepared by means of it. Another object is toprovide such a process in which organic acids containing the acidic groups for the esters may be used directly without the trouble and expense of preparing their anhydrids or chlorids. A further object is to protion of the acidic groups available for the cellulose ester is actually combined into the ester, without being wasted. Another object is to provide a cellulose-esterifying process in which, as a main initial ingredient, there is an anhydrid of an organic acid, which anhydrid does not contain a cellulose-esterifyin group or hydrolyze to an acid containing such a gr0up',-in other words, the anhydrid impels vesterification without contributing any groups to the esters produced.

Another object of the invention is to provide a relatively simple process which will be rapid economical and easilycontrolled. A still iurther object is to provide a process which will. esterify, not only easily esterified cellulosic bodies, such as hydrocellulose and reverted cellulose, but can also and referably utilize substantially undegrade cellulose, such as cotton, surgical cotton wool, tissue paper from cotton stock, and even sulfite wood pulp, thereby producing cellulose esters of higher quality. Another object is'to provide such a process in which the ingredients form a liquid active esterifying bath at temperatures which do not substantially impair the cellulose or the cellulose esters. A still further object is t6 provide a process which,

as it proceeds, produces a solvent that helps to keep the esteriffiing ingredients in proper solution. Other 0 jects will hereinafter ap-- ear. P We have found that these objects may be attained, in general, by subjecting the cellulosic materialto'the coaction of an organic acid containing a cellulose-esterifying group and an organic acid anhydrid which impels stituted fatty acid anhydrids.

Application flld March 28, 1927. Serial m5. 179,177.

such esterification without itself supplying any cellulose-esterifying groups as disclosed in our cop ending application 179,176. By 7 the term cellulose-esterifying groups, we refer to those which are capable of combining with the cellulose under the conditions of our process; The organic acids which we canemploy for furnishing such groups can be selected from the group which conslsts of the unsubstituted aliphatic monocarboxylic acids including the cycloparaffinic, the aromatic I monocarboxylic acids and the aralkyl monovide such a process in which a high proporcarboxylic acids. Typical anhydrids which can be used in our process to impel esterification, without furnishing cellulose-esterfying groups, include the halogen or alkoxy sub- Of these, the ones having less than ten carbon atoms are the most convenient to use. In fact, we prefer to use a chlorinated acetic anhydrid, the

anhydrid of monochloracetic acid (hereinafter referred to for convenience as chloracetic anhydrid) being as advantageous as any other and less expensive.

The time of the process is shortened and the results are more. advantageous when a catalyst is used. While we may employ any of. the catalysts which have hitherto been used successfully in the production of cellulose acetate from acetic anhydrid, we prefer to utilize the milder ones, such as the perchlorates disclosed in'the application of Carl J. Malm, Serial No. 137 ,385, filed September 23rd, 1926 for process of making cellulose esters of organic acids. Zinc chlorid'is satisfactory, but we prefer magnesium perchlorate. We can also use red phosphorus. and chlorine,see U. S. Patent No. 1,591,590, Webb and Malm, July 6th, 1926.

of the esterifying bath, but below temperatures at which the cellulose, or the esters made from it, are degraded. Such degradation is indicated by brittleness of films prepared from the esters. It spould be noted that when the ingredients o our baths are mixed together the mixture usually has a lower melting point than the melting points of the ingre i ente, taken alone." It should taining less than ten a strong solvent action upon the acids which we employ,

, cated in the appended claims.

further be noted that the halogen substituted fatty acid anhydri'ds, especially those concarbon atoms, have as stated above. For instance, chloracetic anhydrid has a good solvent action on such difiiculty soluble materials as stearic acid. Moreover, the monochloracetic acid, which is formed from said anhydrid during the esterification is likewise a strong and satisfactory solvent of the acids. There is, therefore, no danger of premature precipitation of the ingredients as the reaction proceeds. While the general range of available temperatures is indicated above, we find it especially convenient to work between 50 C. and 80 (1., according to the particular acids and halogenated'fatty acids anhydrids employed. As will be seen by the examples hereinafter given, rapid esterification may be accomplished in a comparatively short time, Without degradation of the product, at a temperature of 60 to C., when acetic anhydrid and magnesium perchlorate are employed.

Our process can utilize cellulosic materials from any of the sources customarily used in the manufacture of esters, such as cotton fiber tissue paper, .clean cotton, surgical cotton wool, and even sulfite wood pulp, (pref :rably bleached). These materials, especially the cotton materials, are undegraded when they enter our process and yield esters which are likewise substantially unimpaired or undegraded, as evidenced by the flexibility of films prepared from them. But our process is likewise applicable to cellulosic materials which have so-callecl hydrocellulose, reverted cellulose, such as from the viscose or cuprammonium processes and lower cellulose nitrates, acetates, formates, or ethers still containing esterifiable hydroxyls.

We shall now give numerous examples of our process by way of illustration, but it will be understood that our invention'is not limited to the details thus given, except as indi- Taking one of the simplest cases, a bath is prepared by mixing 25 parts by weight of glacial acetic acid with 30 parts by weight 0 drid and 0.05 parts of magnesium perchlorate trihydrate. Into this, are well mixed, there is thoroughly incorporated 5 parts by weight of clean cotton. During the esterification this bath is kept between 60 to 65 C. The completion of acetylation is indicated by the disappearance of the cotton fibers, the reaction mass becoming homogeneous. This occurs comparatively rapidly,say in about three'hours. The completed ester is obtained from the bath by treatment which follows customary practice. For example, the bath may be poured, with stirring,

been chemically affected, such as chloracetic anhy- I after the ingredients into cold methyl alcohol, or any other solvent of the fatty acid, which is not a solvent of the product. Precipitation in cold water is, therefore, possible with our process. Where the latter is employed, the organic acids in the solution may be obtained either by extraction with volatile organic solvents or by 0011- centration, neutralization, evaporation and treatment of the salts thus obtained, as is well known to chemists skilled in the-art. lVhere precipitation into an organic liquid takes place, the acids, acid, may be recovered by fractional distillation, under a partial vacuum, when necessary. Some of the chloracetic values may be alternatively recovered by conducting air through the reaction mass, while the latter is strongly agitated, and then conducting the air to a condensing chamber to remove chlora cetic vapors from it, this air being warmed and then recirculated through the reaction mixture. Here again the operating temperature is k pt low enough to avoid injuring the ester, preferably well under 130 C. See U. S. Letters Patent No. 1,494,816, Seel, May 20th, 192-1, No. 1,560,620, Sulzer, November 10th, 1925, and N 0. 1,516,225, Webb, November 18th, 1924, for examples of similar recoveries.

or convenience we have arranged the following examples in tabular form:

u R g Solubillties of final pro- Q '5, g a. ducts at room temper- ;I 6 w .c: ature .g B 03 5.5,

we B 2 :1 E q 3 5 o 3 Nameoftheacld 3 n :3 u E :5 g E3 8 0 Fi 5 Q a! O 01" M s L q ,9. a :1 C1 "5 "6 "5 8 E4: 5 g 2. s s s as o 8 8 E f. 5 a s s s s .s s e e m m e m a E El .5 3 E 5 Hrs. 25 5 30 0.05 a 25 5 30 0.05 3 1o 3 20 0.05 4 15 3 25 0.05 4 15 3 25 0.05 4 (n) 153250.054++++++ n-ca'prolc 20 5 00 0.05 4 n-l1eptylic 18 4 55 0.05 8 Caprylic 25 5 G0 0.05 5 Pelargonic" 25 5 (:0 0.05 5 25 5 00 0. 05 5 20 3 20 0.05 4 25 4 00 0.05 4 15 2 60 0.05 24 15 2 G0 0.05 24 15 5 30 0.05 5 Cyelohexane-carboxylic 10 2 15 0.02 3 Benzoic 15 3 20 0.05 8 o-methoxy-benzoic 10 2 15 0.02 4 o-chloro-benzoic- 10 2 15 0.02 5 Acetylsallcylic 20 2 20 0.05 10 Phenylacetic" 15 3 20 0.05 7 Hydroeinna 15 3 30 0.05 3 Cinnamic 5. 13 3 40 0.05 -5 Stearlc (comm. 3 Acetic 6 40 0 1 o niethosybengg e g 15 0 02 7 Acetic" 15 2 20 0.021 3 Acetic" 10 2 20 0.05 0

r Trichloracetic anhydrid was used in place of the monnchloracctic. Betabrompropionie anhydrid was used in place of the monochloroacetie.

(a) Soluble in warm ligroin, insoluble at room temperature.

especially the chloracetic;

benzol.

and fourth examples from the bottom'of the.

In all of the above examples the workin tem rature is kept between 60 and 65 In t e six columns at the right, which indicate the solubilities, a minus sign indicates that the ester, which is produced, does not dissolve in the particular liquid inquestion, at least not to any readily detectable or useful extent. A plus sign indicates that it does have a useful solubility in such a solvent at room temperature. For example, the cellulose acetostcarate produced in the fourth from the last example in the table is soluble in acetone and chloroform but insoluble in As will be evident from the third table, we may obtain mixed esters by using mixtures of the acids in any desired propor'- tions. The third from the last example gives cellulose aceto-orthomethoxybenzoate. In the case of the unsubstituted monocarboxylic aliphatic acids containing'a double bond, the latter should preferably be situated in the alpha-beta osition relatively to the carboxyl grollip. hus crotonic and cinnamic acids act wel Moreover, we. may usefully have present chloracetic acid at the start of the reaction in addition to the amount of such acid formed during the reaction. For example, we may re are a bath by mixing 300 parts by weight 0 oracetic anh drid, 100 parts by weight of chloracetic aci 185 parts of stearic acid,

parts of acetic acid, and 0.5 parts of mag- .nesium perchlorate. Into this is stirred 25 parts by weight of cellulose and the reaction mixture kept for about 8 hours at 60 to 65 C. A clear dope is thus obtained and the .mixed cellulose ester is separated, and the other ingredients recovered, as indicated hereinabove. The mixed ester is soluble in acetone and insoluble inbenzene. Analysis shows it to contain 40% of stearyl and palmityl groups and 22.% of acetyl groups. Its

acetonesolutions can be formed into films which are colorless, transparent and of very hi h flexibility either wlth or without the a dition of plastifyings'ubstances, such as tri henyl phosphate. another example, we may mix 155 parts by weight of chloraceticanhydrid, 190 parts by weight of chloracetic acid, 92 parts of stearic acid, 20 parts of acetic acid, and 0.3

parts of magnesium perchlorate. N25 parts by weight of cellulose are treated in this mixture at to C. until a clear dope is formed, say for about 12 hours. The ester acetyl groups.

65 are'substituted in wlfole or .in part the coranhydrids are potentlal acids and when we hereinafter refer to the acids which furnish the cellulose-esterifyinggroups, we shall, for convenience, indicate by that term either said acids, or their anhydrids, or mixtures of them, For example, we may prepare a bath of 20 parts by weight of chloracetic anhydrid, 30 parts of chloracetic acid, 7 arts of stearic acid, 3 parts of acetic'anhydi'id and 0.1 part of magnesium perchlorate. In this are treated 4 parts by weight of cellulose for about 5 hours at 60 to 65 C. When a clear dope is formed, the cellulose ester is separated, as hereinabove described. This mixed ester is soluble in acetone, chloroform, and insoluble in-benzene, being an acetostearate of cellulose.

While formic acid has certain chemical properties-not found in the other fatty acids, our process can be carried out with it. For example, 20 parts b3 weight of-formic'acid (85% strength) an 40 parts of chloracetic anhydrid are warmed at 50 C. for one hour and cooled down to 30 C. Five parts by wei ht of cellulose are added to the mixture wit stirring and the mixture kept at 35 to 40 C. for 96 hours. The mixture is poured into water, with agitation to precipitate the cellulose formate, which can be washed. It is completely soluble in acetone at room tem- "perature, insoluble inchloroform and contains about 25.5% of the group HCO, corresponding closely to a diformate. While the reaction is preferably carried out for 96 hours, a clear dope may-be formed as early as24 hours; if the product be isolated at this sta c, it is found to contain only 19% of the ormyl group and to be insoluble in acetone.

Using the same reaction mixture and conditions in the receding example, we can,

after 48 hours 0 the reaction, add to the mixture 10 parts by, weight of formic acid with 20 parts of chloracetic anhydrid and the reaction condu'cted 48 hours more. This gives,

after precipitation and washing, a product somewhat higher than a diformate, which is soluble in acetone but not in chloroform and maycontain 27.6% of the H00 group.

Moreover, the cellulose formate thus produced, maybe further esterified by our process to obtain mixed esters. For example, 4 parts by weight of an above described acetone-soluble cellulose formate are added toa mixture of 15 parts by weight of stearic acid, 20 parts of chloracetic anhydrid and .05

parts of magnesium perchlorate and the mass warmed and kept at 60 to 65 C. for about 72 hours. This maybe precipitated in warm methyl alcohol. The mixed formostearate is soluble at room temperature in acetone, chloroform, or benzene, but insoluble in ligroin, ether-,or carbon tetrachlorid.

As an example of the use of red phosphorus and chlorine to catalyze the reaction, we note the following: Into 25 parts by weight of acetic acid and 35 parts of chloracetic anhydrid there are mixed 5 parts of cotton cellulose, and 0.2 parts of red phosphorus. This is treated with chlorine bubbling through it until the absorption of chlorine ceases. The mixture is then warmed between to 68 C. until it becomes homogeneous. It is then poured into water and the product isolated by' the usual known methods. This yields chloroform-soluble cellulose acetate, whichmay be hydrolyzed in the usual way.

The halogen substituted anhydrids of the fatty acids are notthe only substituted anhydrids of these acids which impel esterification without containing esterifying groups. Certain groups, such as the alkoxy group, behave like a halogen group in this respect when substituted in the same place in the fatty acid anhydrid. Take methoxyacetic anhydrid, for example. Mix 15 parts by weight of it with 10 parts of acetic acid and 0.1.0 parts of magnesium perchlorate and warm to 60 to 0. Into this are stirred 2\parts of cellulose, say tissue paper (cotton stock), and after 50 hours at the above temperature a clear dope results which, upon pouring into methyl alcohol, etc., yields a product soluble in chloroform and insoluble in acetone,in other words, it yields fully acetylated cellulose which is, upon analysis, found to be substantially free from methoxy groups. Ethoxyacetic anhydrid and its higher alkyl homologues act like methoxyacetic anhydrid.

It is a useful feature of our invention that it may be employed with commercial organic acids. For example, commercial stearic acid contains not only the pure stearic acid but also palmitic acid in considerable quantities. During the esterfication, both of these acids enter from the mixture into the product and thus mixed esters may be prepared from commercial mixed acids. In the same way the saturated acids of cocoanut oil contain several acids of the fatty series, such-as lauric and myristic, and all of these enter into the ester when such a mixture is utilized in our process. While we have also illustrated two mixed esters in which acyl groups of high and low molecular weight are used, namely, acetostearates and aceto-methoxybenzoates, it will be evident that any two or more of the organic acids in the group from which we make our selection, as specified above, may be used in forming mixed esters. This is extremely valuable, because, as indicated by the above examples, the solubilities of the products in different commercial organic solvents can be regulated by a proper selection of the esterifying acids and their proportions.

While the chloracetic anhydrid is preferred, the di and tri-chloracetic anhydrids 1,ss0,sos

brom propionic and butyric anhydrids willoperate, but they are too expensive to compete commercially. The corresponding iov dine substituted acetic, propionic and butyric anhydrids are likewise expensive without proportional benefit. But whichever of the halogen substituted fatty acid anhydrids is employed, it is a characteristic of each of them that it will not contribute groups to the ester. Apparently the presence of the halogen in the molecule is the cause of this. Any substituted group in the anhydrid which prevents it from contributing groups to the ester can be used, such, for instance, as the methoxy group in methoxyacetic anhydrid. When properly purified, all of the esters produced by our process, contain no halogen atoms, except the ester of orthochlorbenzoic acid, which, of course, does not derive its halogen from the chloracetic anhydrid or chloracetic acid but only from the original orthochlorbenzoic acid.

The proportions in the above examples can be varied over a considerable range. The amount of chloracetic anhydrid can be greatly reduced to lessen the expense. It will be noted that our process is very economical in its use of the esterifying acids. For example, in the making of cellulose stearate from commercial stearic acid in the above table, the amount of stearic acid is only about 25% above that theoretically required. The yield, on the basis of the original cellulose is of the order of 250%.

It is a great advantage of our process that the esterification, especially of the mixed esters, can be carried out in one operation or by a single treatment in a single bath. If it be desired, for special reasons, to carry it out in a series of operations, our process can, of course, be used, the treatment being stopped at the different stages. Cellulose, which has been partially esterfied, eitherby our method or by other methods, can be further or completely. esterified by our method. For instance, as the cellulosic material, partially acetylated or nitrated cellulose may be substituted in equimolecular proportions for the cellulose in the above examples. Higher acid groups may be introduced in this way and gra hic films, of filaments for making rayon, of lacquers, of artificial leather, of plastics and other fields in which. cellulose esters have hitherto been employed. Many of the esters of the higher fatty acids and the aceto hig'her fatty acids have qualities which 'give them exceptional adaptability in this art. For example, they give flexible film or filaments without softeners or plastifiers; but the acetone-soluble or chloroform-soluble plastifiers, heretofore used with cellulose acetates, may be used with them. i Triphenyl and tricresyl phosphates are good examples of the large number which can be used within-the usual range of proportions.

acetate by means of a common solvent. They can be backed with a cellulose acetate layer or with hygroscopic nitrocellulose coatings to prevent static, and these backings may have their electrical conductance improved by containing hygroscopic compounds.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

1 The process of making cellulose esters which comprises treating cellulosic material with an esterifying bath containing a halogen-substituted fatty acid anhydrid and an organic acid which contains an acyl group and which is selected from the group-which consists of, first, the unsubstituted aliphatic monocarboxylic acids including the cycloparafiinic, second, the aromatic monocarboxylic-acids, and, third, the aralkyl monocarboxylic acids.

2. The process of making. cellulose esters which comprises treating cellulosic material .vith an esterifying' bath containing as a source of esterifying groups at least one or ganic acid which contains an acyl group and which is selected from the group which consists of, first, the. unsubstituted aliphatic monocarboxylic acids including the cycloparaflinic, second, the aromatic monocarboxylic acids and, third, the aralkyl monocarboxylic acids, and also containing as an impellent of esterification a halogen-substituted fatty acid anhydrid having less than ten carbon atoms.

3. The process of making cellulose esters which comprises treating cellulosic material with an esterifying bath containing as a source of-esterifying groups at least one organic acid which containsan acyl group and which is selected from the group whichconsists of, first. the unsubstituted aliphatic monocarboxylic acids including the cycloparaffinic, second, the aromatic monocarboxylic acids, and also containing a halogen substituted acetic anhydrid to impel esterification and to form the corresponding halogen-substituted acetic acid as a solvent.

4. The process of making cellulose esters which comprises treating cellulosic material with a liquid esterifying mixture containing They can be' mixed or laminated with cellulose nitrate oran organic acid selected from the group which consists of, first, the unsubstituted aliphatic monocarboxylic acids including the cycloparafiinic, second, the aromatic monocarxylic acids, and, third, the aralkyl monocarboxylic acids, and also containing chloracetic anhydrid.

5. The process of making cellulose esters which comprises treating cellulosic material with an esterifying bath containing an organic acid which contains an acyl group and which is selected from the group which consists of, first, the unsubstituted aliphatic monocarboxylic acids including the cycloparaflinic, second, the aromatic monocarboxylie acids, and, third, the aralkyl monocarboxylic acids, and a'substituted fatty acid anhydrid which impels esterification of the cellulose by said first-named acid, but is prevented by the presence in it of the substituent group from contributin groups to-the ester.

6. The process of mafiing fatty acid esters of cellulose WhlQh'COHlPl'lSGS treating eel-p lulosic material with an esterifying bath containing a halogen-substituted fatty acid anhydri and an unsubstituted fatty acidl 8. The process of makingcellulose esters which comprises treating cellulose with .an

'esterifying bath containing an excess of organic acid over the amount requiredin the esterification reaction, said acid containing an acyl oup and being selected from the point of the bath but below the temperatures at which the cellulose .and the ester are impaired.

9. The process of making fatty acid esters of celluose which comprises treating cellulose with an esterifying bathcontaining an unsubstituted fatty acid, and a halogen-subsid tuted fatty acid anhydrid containing less; than ten carbon atoms.

10. The process of making fatty acid esters ofcellulose which comprises treating cellulose with an bath containin chloracetic anh drid, an an unsubstitu fatty acid, sai treatment being conducted abota the melting point of'the bath but below grolgi w ich consists of, first, the unsubstialip 11. The process of making stearyl-contain- I ing' cellulose esters which comprises treating chloracetic anhydrid, and stearic acid, the treatment being conducted above the melting point of the bath but below 80 C.

12. In the process for the manufacture of esters of cellulose with the higher homologues of acetic acid, the step which comprises treating cellulose with chloro acetic acid anhydride and a higher homologue of acetic acid.

with the addition ofa catalyst.

13. In the process for the manufacture of esters of cellulose with the higher homologues of acetic acid, the step which comprises treating cellulose with chloro acetic acid anhydride and a monobasic fatty acid containing at least 3 and not more than 4 carbon atoms with the addition of a catalyst.

14. The process of making fatty acid esters of cellulose which comprises treating cellulose with an esterifying bath containing chloracetic anhydride, monochloracetic acid and a monobasic fatty acid containing at least 3 and not more than 4 carbon atoms.

15. The process of making a propionic ester of cellulose which comprises treating cellulose with an esterifying bath containing propionic acid, chloracetic anhydride and monochloracetic acid.

'16. The process of making fatty acid esters of cellulose which comprises treating cellulose with an esterifying bath containing an unsubstituted fatty acid, chloracetic anhy-' dride and monochloracetic acid.

17 The process of making fatty acid esters of cellulose which comprises treating cellulose with an esterifying'bath containing a higher homologue of acetic acid, chloracetic anhydride and monochloracetic acid.

18. The process of making fatty acid esters of cellulose which comprises treating cellulosic material with an esterifying bath containing a substituted fatty acid anhydride vWhich impels esterification of the cellulose,

and a mono-basic fatty acid containing carbon atoms.

19. The process of making fatty acid esters of cellulose which comprises treating cellulosic material with an esterifying bath containing chloracetic anhydride and a mono-- basic fatty acid containing 3-4 carbonatoms.

20. The process of making a fatty acid ester of cellulose which comprises treating cellulosic material with an esterifying bath containing propionic acid and chloracetic anhydride.

21. The process of making a fatty acid ester of cellulose which comprises treating cellulosic material with an esterifying bath containin chloracetic anhydride, monochloracetic aci and ropionic acid;

Signed at Roc ester, New York, this 23rd day of March, 1927.

I HANS T. CLARKE. CARL -J. MALM. 

